Arkansas Total Maximum Daily Loads (TMDL)

Some of the state’s impaired waterways on the 303(d) list are tapped for corrective action to improve their
water quality. Some require the development of a TMDL – Total Maximum Daily Load.

A TMDL is a calculation developed for some waters that are not meeting or are at risk of not attaining water
quality standards. The TMDL calculates the maximum amount of a constituent a waterbody can receive and still
meet the standards.

A TMDL accounts for both point source and nonpoint source discharges.

Calculations are performed by various models that predict safe levels of contaminants based on worst-case
conditions and providing a margin of safety. The calculated safe amounts then may be allocated to point
source discharges as a wasteload allocation and to nonpoint sources as a load allocation. This constitutes
a TMDL. Permit limits are set according to a stream’s TMDL.

ADEQ has been working in conjunction with the Arkansas Natural Resources Commission (ANRC) to target resources
for water quality improvements within the state. The ANRC is responsible for developing and implementing Arkansas’
Nonpoint Source Pollution Management Program. ANRC prioritized ten basins in Arkansas using stakeholder involvement
coupled with a science-based process. For TMDL prioritization, nine of the ten ANRC basins were chosen because they
have impairments that carry from ADEQ’s 2008 303(d) list to the Draft 2014 303(d) list. ADEQ plans to work towards
TMDL or alternative plan development for the currently selected basins by 2022.